1. Field of the Invention
This invention relates to the conversion of scrap polyurethane to useful polyols and is more particularly concerned with a process for the conversion of scrap flexible polyurethane foam, derived from a polyether polyol, to polyols which are reusable in the preparation of cellular polyurethanes.
2. Description of the Prior Art
The amount of scrap polyurethane foam which is being generated as trim, dust and the like from foam cutting operations, is a problem of increasing concern. The disposal thereof in solid waste form represents an environmental pollution problem as well as an economic one. The recovery and reuse of scrap rigid polyurethane foam has recently become possible through the process described in U.S. Pat. No. 3,738,946. The latter process involves heating the scrap foam with a mixture of aliphatic diol and a minor amount of dialkanolamine to produce a homogeneous polyol mixture capable of use, in its entirety, as a polyol component in the production of new polyurethane foam. The prior attempts to solve the problem of recovery of scrap foam are discussed in some detail in the above cited patent and will not be reviewed here.
Unfortunately the process of the above cited patent, which is entirely satisfactory for rigid foams, cannot be applied successfully to the recovery of the major class of flexible foams, namely, those derived from a polyether polyol. Thus, the process of the above patent, when employed with scrap from flexible, polyether-based foams, gives a product which separates into two layers, one of which is a polyol and the other appears to be a polyamine. The latter requires to be separated from the former and is not useful in the preparation of further polyurethane foams, although it has uses as a curing agent for epoxides and the like.
Substantially the same result is reported in U.S. Pat. No. 3,632,530 which describes the treatment of scrap flexible polyether-based polyurethane foam by heating in the presence of an aliphatic glycol and, optionally, a tertiary amine. The product separates into two layers one of which is polyol and the other is said to be polyamine. The latter is separated and shown to be useful as an amine curative for epoxy resins and for isocyanate-terminated prepolymers. As is evident from Example 9 of the above cited patent, there is no such problem with a polyester-based flexible foam. The latter gives rise to a homogeneous product which shows no tendency to separate into two layers.
Unfortunately, however, the bulk of the flexible foams currently produced commercially are derived from polyether polyols, and scrap from such foams has not so far been converted successfully to a homogeneous product which is usable in its entirety as a polyol component for the preparation of new polyurethane foam.
We have now found that, contrary to previously reported experience, it is possible, by careful choice of reactants, and of proportions thereof, and of reaction conditions, to convert scrap, polyether-based flexible polyurethane foam into a homogeneous mixture of polyols, which mixture does not separate into different components but can be used in its entirety as part, or the whole, of the polyol component employed in the preparation of new polyurethane foam.